Piper Alpha Platform, North Sea, United Kingdom
Piper Alpha is an offshore oil and gas platform that suffered an explosion in July 1988, still regarded as the worst offshore oil disaster in the history of the UK. The 25th anniversary of the disaster was commemorated across the country in July.
The accident killed 165 out of 220 crew members, plus two crew from the standby vessel Sandhaven. The accident was attributed mainly to human error, and was a major eye opener to the offshore industry regarding safety issues. Property damage from the explosion was estimated to be approximately $1.4bn.
Piper Alpha, owned by Occidental Petroleum, started production in 1976 from the Piper Oilfield, which is owned by the OPCAL joint venture. It was initially constructed as an oil production platform and was later converted to facilitate gas production with a new gas recovery module added. Piper Oilfield produced oil from 36 wells.
Construction details and specifications of Piper Alpha Platform
Piper Alpha Platform was constructed in two sections by McDermott Engineering and UIE at Ardersier and Cherbourg respectively. The assembly of the two sections was carried out at Ardersier. The gas processing system of the platform comprised two high-pressure condensate pumps.
The platform was around 300m high and was modular in design, comprising of four main operating areas. The operating areas were separated by firewalls and the platform was equipped with both diesel and electric seawater pumps to supply water to its automatic firefighting system.
The platform had a capacity to accommodate more than 200 people, and featured a helideck. The height of the helideck from the water was around 175ft.
The platform was placed at the Piper oilfield, around 273km north-east of Aberdeen. The offshore oil and gas platform pumped processed crude oil from the oilfield to Flotta Terminal, located on the Island of Orkney. The export oil lines from the new Tartan and Claymore platforms were further connected with Piper's oil export line to the Flotta Terminal.
The platform later served as a hub which processed its own gas, collected gas from the Tartan Platform, and pumped the gas onto the MCP-01 Platform. Piper Alpha was also linked with Claymore via a gas pipeline which received and supplied gas to the latter for gas-lift purposes.
Events leading to the accident on Piper Alpha
The accident was primarily caused by maintenance work simultaneously carried out on one of the high-pressure condensate pumps and a safety valve, which led to a leak in condensates.
After the removal of one of the gas condensate pump's pressure safety valve for maintenance, the condensate pipe remained temporarily sealed with a blind flange as the work was not completed during the day shift. Not aware of the maintenance being carried out on one of the pumps, a night crew turned on the alternate pump. Following this, the blind flange including firewalls failed to handle the pressure, leading to several explosions.
The fire at the platform intensified due to the failure in closing the flow of gas from the Tartan Platform. The automatic firefighting system had remained deactivated since divers worked underwater before the incident. Helicopter operations were hampered due to the amount of heat and smoke.
Cullen inquiry into the platform explosion and recommendations
Following the tragedy, an inquiry into the accident commenced in November 1988 headed by Lord Cullen, which was published in November 1990. The inquiry was conducted in two parts. The first part studied the causes of the tragedy and the second part presented recommendations to avert future occurrence. It presented 106 recommendations for changes to North Sea safety procedures.
The inquiry brought about great changes in the offshore industry with regard to safety management, regulation and training. A major impact was responsibility for North Sea safety shifting from the Department of Energy to the Health and Safety Executive. Also, automatic shut-down valves were made mandatory on rigs, to starve a fire of fuel.
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